Powder applicator for electrophotographic apparatus



United States Patent 1111 3,536,043

[72] Inventors Rudolf Eppe [50] Field of Search 1 18/637, Taui'kirchen; (Misc), (C). (LX), 629,627,626, 398, 312; Karl Hartwig, Munich; and Franz Fruth, l 17/ (inquired), 17, 17.5; 239/681 689, 223 Unterpfalfenhofen, Germany 224; 222/318, 410, 41 l 21 A 1. NO. 737,442

lZZi Fil gd June 17, 1968 4 References Cited [45] Patented Oct. 27, 1970 UNITED STATES PATENTS 1 Assignee AGFA-Gevaerl Akfiengesellschaft 2,789,926 4/1957 FlnhOli. et al 1 l8/308X Leverkusen, Germany 3,349,750 10 1967 DOnalleS... 118 637 [32] Priority J l 1970 3,435,803 4/1969 Donalies l l8/637 Primary ExaminerMorris Kaplan Attorney-Michael S. Striker ABSTRACT: The developing powder of an electrophoto- 1 graphic apparatus is moved out of a container by a rotary body having an inner surface of revolution which flares upwardly so that due to the action of the centrifugal force the powder is [54] POWDER APPLICATOR FOR 3 ELECTROPHOTOGRAPHIC APPARATUS l 8 Claims 2 Drawing Figs moved out of the upper open end of the body into a vibratory [52] US. Cl 118/637, distributor which distributes the powder onto a photoconduc- 1 18/312, 239/224 1 tive surface carrying a latent electrostatic image which is [51] Int. Cl B05b 5/00 developed by the applied powder.

\\\\ TI A ,1 7a 111 1,1 ,1, 1 I n1 ,1,,,, l 7c 7f 7a Patented Oct. 27, 1970 INVENTORS RUDOLF EPPE KARL HART WIG FRANZ FRUT H llll I! (all POWDER APPLICATOR FOR ELECTROPIIOTOGRAPHIC APPARATUS BACKGROUND OF THE INVENTION The present invention relates to electrophotographic apparatus in which a photoconductive layer carrying a latent electrostatic image is developed by the application of a powder adhering to the latent image and consisting preferably of a mixture of a carrier powder and a dye.

In accordancewith the prior art, the developing powder is transported by conveyors carrying scoops out of a lower container to a portion of the photoconductive surface located above the container. Developing apparatus of this type is expensive, but nevertheless does not fully assure a completely uniform distribution of the powder on the photoconductive surface.

SUMMARY OF THE INVENTION It is one object of the invention to provide a powder applicator for electrophotographic apparatus which is inexpensive, and capable of procuding a uniform flow of the developing powder so that the same is uniformly distributed over the photoconductive surface and the latent electrostatic image thereon.

Another object of the invention is to provide a powder applicator of simple construction which reliably operates.

Another object of the invention is to provide a powder applicator which recirculates excess developing powder not adhering to the latent image of the photoconductive surface.

Another object of the invention is to use centrifugal force for raising the developing powder from a lower level to a higher level, and for simultaneously moving the powder in a completely uniform and constant stream.

With these objects in view, an embodiment of the invention comprises a hollow body having between its lower and upper ends an inner surface of revolution with a substantially vertical axis whose diameter increases in upward direction, supply means for supplying a developing powder into the lower end,

and preferably including a container for the developing powder, drive means for rotating the hollow body so that the centrifugal force moves the powder upward on the inner surface of the hollow body and out of a top opening of the same, and photoconductive means, such as a photoconductive layer on a copying cylinder, disposed for receiving the powder moving out of the top opening and passing through a vibratory distributor so that a latent image on the photconductive layer is developed. 7

The lower end of the hollow body has a bottom opening and is located under the level of the developing powder in the container so that the powder enters into the lower end and rests on the inner surface whereby it is subjected to the action of the centrifugal force.

In the preferred embodiment of the invention, a vibratory distributor casing surrounds the upper end of the hollow body and receives the powder driven out of the top opening of the hollow body by the centrifugal force. The vibratory distributor has an outlet in the proximity of the photoconductive means for applying the powder to the same.

A rotary hollow body according to the invention, which may have paraboloid or frustoconical shape, is easily manufactured and is subject fewer disturbances than a scoop conveyor according to the prior art. The powder particles rotate wth inner surface of the hollow body, and are pressed by the centrifugal force onto the same, and due to the upward widening of the diameter of the inner surface, they flow apart to form a uniform layer whose thickness decreases in upward direction. Depending on the slant of the inner surface in axial direction, a force component of the centrifugal force overcomes the downward action of gravity and also the friction force acting against displacement of the powder particles on the rotating surface.

When the powder particles have travelled to the upper open circular end of the rotating inner surface, they are thrown out in tangential direction, which further improves the uniform distribution of the powder into the vibratory distributor casing. The uniform stream of ejected powder particles is transported by the vibratory distributor casing in a continuous horizontal layer to the photoconductive surface.

The amount transported by the rotary hollow body out of the supply container and onto the photoconductive surface, can be influenced by varying the angle of the rotary inner surface, the speed of rotation of the same, and by curving the inner surface of the hollow body in axial planes. Preferably, slanted blades are mounted at the lower end of the hollow body for throwing powder onto the rotary inner surface. By

varying the shape and slant of the blades, the amount: of

powder entering the hollow body can be varied.

In a preferred embodiment of the invention, a box-shaped distributor has a bottom plate surrounding the upper end of the rotary body and receiving the ejected powder. The boxshaped distributor has a narrow outlet slot in proximity to the photoconductive surface and extending parallel to the same. The narrow slot dauses a damming-up of the powder in the distributor so that the stream of powder reaching the photoconductive surface is even more uniformly distributed.

Due to the uniform flow of a thin layer of powder onto and downwardly along the photoconductive surface, very accurate powder images and consequently copies with a clean background and sharp definition are obtained.

The damming up of the developing powder in the region of the outlet slot of the distributor can be influenced by selecting an outlet slot of such a width that at all times a certain amount of developing powder rests on the bottom face of the distributor. The amount of powder in the distributor, and the mass of the distributor itself, assure a vibration of the distributor at a frequency close to resonance.

In a preferred embodiment, surplus of the developing powder flows downwardly along the photoconductive surface of a copying cylinder. and is gathered in the region of a lower portion of the cylinder by an edge of the powder container into which the lower end of the hollow body projects. Assuming that the axis of the cylinder is horizontal, the outlet slot of the distributor is located near the highest generatrix of the cylinder, and the edge of the container is located below a horizontal plane passing through the cylinder axis.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING DESCRIPTION OF THE PREFERRED EMBODIMENT The cylinder 1 of an electrophotographie apparatus has a cyldrical peripheral outer layer and surface la which is charged by a corona discharge device, not shown, and is exposed by the image of a master or original to be copied whereby a latent electrostatic image is formed on the photoconductive layer la, as is well known to those skilled in the art.

A container 2 is located below a horizontal plane passing through the axis of cylinder 1 and has a side wall 2a ending in an edge located in close proximity to the outer surface la. Container 2 contains a supply of a developing powder, and is supported by supporting means, not shown, container 2 has a central recess in its bottom plate in which the lower end of a drive shaft 3 is rotably supported. The upper end of drive shaft 3 is mounted in stationary bearings of a support 10 and is connected with the rotor of an electromotor 6 which is carried by support 10.

A hollow body 4 of substantially frustoconical shape has a lower end located in container 2 and having a bottom opening 4c located under the level of the powder 5 in container 2. The lower end portion 4:! of the hollow body 4 is curved in axial planes passing through the axis of the inner surface of revolution 4f of the hollow body 4. Blades 4a are secured to the lower end of drive shaft 3 and to the lower end portion 4d so that powder entering through the bottom opening 4c is scooped up and guided by blades 4a toward the inner surface f- When shaft 3 is rotated by motor 6 at a sufficient speed, the cetrifugal force urges the powder particles to move upward along the inner surface 4f and to flow in tangential direction over the horizontal flange 4b at the upper end of the annular top edge of the hollow body 4. Due to the fact that the diameter of the inner surface 4f is greater at the upper end than at the lower end of the body, the upwardly travelling powder is forced to spread out and to form a layer whose thickness gradually decreases in upward direction so that a thin sheet of loose powder particles is thrown by the centrifugal force away from flange 4b.

A vibratory distributor casing has a bottom wall 7 with an annular upright collar 7b surrounding the upper end of the hollow body 4 and being located under flange 4b. Bottom wall 7 is surrounded by side walls 7a which are higher than flange 4b and collar 7b. The top of distributor 7 is closed by a top wall 7d. One straight side wall 7e is located above the photoconductive outer surface la, and has a lower edge 7c forming together with an edge 7fof the bottom wall ofthe distributor 7, an outlet slot extending in axial direction along a generatrix of the cylindrical surface la, and near the highest generatrix of the same.

An electric vibrator 8 is mounted on a support 10a and connected with the distributor 7 to vibrate the same so that the powder accumulating on the guide surface 7g around the annular collar 7b travels toward the outlet slot 7f and is deposited in a uniform stream on the moving photoconductive surface la whereby a uniform thin layer of powder flows downward almost over the entire upper quarter of the cylindrical surface la over the latent electrostatic image to which the powder adheres to form a transferrable powder image, Those powder particles which are not attracted by the latent electrostatic image continue to flow downward into container 2 since the upper edge of wall portion 2a of container 2 is located below a horizontal plane passing through the axis of the cylinder, and on the right of the left extremity of the cylindrical surface la, as viewed in the drawing, powder returned into container 2 is again raised by the frustoconical inner surface of the hollow body 4 and transported by the vibratory distributor 7 to the photoconductive surface 1 a so that the powder is continuously recirculated.

ln the diagram of FlG.2, the inner surface dfwith an angle a at which the inner surface 4fis slanted to its axis A, is shown. It is necessary for angle a to have a minimum value in order to obtain the upward travelling of the powder particles, and this minimum value of the angel a can be determined as follows:

lt is assumed that r is the radius of the inner surface of revolution 4f at which a powder particle 5a is located, that m is the mass of the powder particle 5a, that g is the gravitational acceleration, that w is the angular velocity of the hollow body 4, and that p. is the coefficient of friction between the particle 5a and the inner surface 4f.

The force of gravity m** g acts downward, and has along the slanted surface 4fa component m**g**cosa. The centrifugal force acting in horizontal direction is m*"w **r. The component of the centrifugal force acting perpendicularly to the surface 4f is m**m **r**cosa. The component of the centrifugal force acting upward along the surface 4f is m""m **r**simr. The component of the force of gravity acting perpendicularly to the surface 4f is m**g**sina. The force com ponents acting perpendicularly to the surface 4f, multiplied by the friction coefficient 2 represent the frictional resistance against movement of the powder particle Be on surface 4f. The upward force component of the centrifugal force, and the downward force component of gravity oppose each other, and it is necessary that the upwardly acting component of the centrifugal force is greater than the downwardly acting component of the force of gravity. This can be mathematically expressed as follows:

1. mw r sin amg'. cos a (mw r cos (xi-mg. sin 01);: This expression can be divided by In and cos 0:. 2. m tang agw r;t g. tang zx 0 from which follows:

3. tang; a(w T-pg.) w 1y+g and the smallest permissible angle can be derived from the following equation:

lf at a predetermined rotary speed or, the angle a is greater than determined from the above equation, the powder will travel in upward direction along the inner surface 4fand pass over its circular upper edge in a tangential stream.

it will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of electrophotographic developing apparatus differing from the types described above.

While the invention has been illustrated and embodied in a powder applicator having an upwardly flaring, rotating surface of revolution for transporting a developing powder to a higher level and for distrubuting the same in a uniform stream, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that from the standpoint of prior art fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence ofthe following claims.

We claim:

l.Powder applicator for electrophotographic apparatus, comprising, in combination, a hollow body having a lower end, and an upper end bounded by an annular top edge forming a top opening, said hollow body having between said lower and upper ends an inner surface of revolution with a substantially vertical axis, the diameter of said inner surface increasing in upward direction; supply means for feeding a developing powder into said hollow body so that the powder accumulates at the lower end of said surface of revolution; drive means for rotating said hollow body about said vertical axis so that the centrifugal force moves the powder upward on said inner surface, over said annular top edge and out of said top opening; photoconductive means adapted to have a latent image and being located on one side of said body; a distributor casing having a bottom wall formed with an opening through which said upper end projects so that said annular top edge is located above said bottom wall in the interior of said distributor casing whereby the powder moving over said top edge rests in a layer in the interior of said distributor casing on said bottom wall, said casing having a side wall confronting said photoconductive means and being formed with an outlet slot opposite the same; and vibrator means for vibrating said distributor casing in a substantially horizontal plane so that the powder on said bottom plate is thrown out of said outlet slot toward said photoconductive means.

2. Powder applicator as claimed in claim 1 wherein said bottom wall is horizontal; wherein said side wall is straight; and wherein said outlet slot is straight, adjacent the top face of said bottom wall, and parallel to said photoconductive surface so that the powder travels through said outlet slot in a horizontal layer toward said photoconductive surface and impinges a horizontal line of the same.

3. Powder applicator as claimed in claim 2 wherein said distributor casing has a top wall and side wall means between said top wall and said bottom wall so that the powder bounces during vibration off said side wall means, forms said layer on said bottom wall, and is ejected through a said outlet slot only in the region of said one side where said photoconductive means is located.

4. Powder applicator as claimed in claim 2 wherein said photoeonductive means has an upper portion located at the level of said outlet slot, and a lower portion so that the powder is applied along said line to said upper portion and flows downward to said lower portion; and wherein said supply means includes means located in the proximity and at the level of said lower portion for receiving surplus powder which does not adhere to said upper portion, and for feeding the surplus powder to said hollow body.

5. Powder applicator as claimed in claim 2 wherein said photoconductive means includes a rotary cylinder having a horizontal axis and a cylindrical outer surface for receiving the latent image; wherein said outlet slot is parallel to said horizontal axis and positioned above the same so that said line extends along a generatrix of the upper portion of said cylin drical outer surface so that the powder applied along said line flows downward along said cylindrical outer surface of said cylinder along the latent image in the region of said cylindrical outer surface above 'a horizontal plane through said horizontal axis.

6. Powder applicator as claimed in claim 5 wherein said supply means include a container located under the lower end of said body and having a straight top edge portion extending along a generatrix of said outer surface of said cylinder adjaeent to the portion of said cylindrical surface located below said horizontal plane so that the powder drops from the generatrix in said horizontal plane into said container; and wherein said lower end of said hollow body is formed with an inlet for the powder located under the level of the powder in said container.

7. Powder applicator as claimed in claim 1 wherein said opening in said bottom wall is bounded by an upwardly projecting collar; wherein said upper end of said body forms an outwardly projecting flange having said top edge and being located above said collar; wherein an edge of said side wall forms the upper boundary of said outlet slot, and is located at a lower level than said top edge; and wherein the top surface of said bottom wall forms the lower boundary of said outlet slot.

8. Powder applicator as claimed in claim 1 comprising blade means disposed in said hollow body only at said lower end; wherein said hollow body has an inlet opening at said lower end thereof; and wherein said supply means include a container under said lower end adapted to contain the powder at a level higher than said inlet opening so that powder entering through said inlet opening into the lower end of said hollow body is thrown by said blades onto said inner surface of revolution. 

